Bug 1927559 (CVE-2021-27135)

Summary:	CVE-2021-27135 xterm: crash when processing combining characters
Product:	[Other] Security Response	Reporter:	Doran Moppert <dmoppert>
Component:	vulnerability	Assignee:	Red Hat Product Security <security-response-team>
Status:	CLOSED ERRATA	QA Contact:
Severity:	high	Docs Contact:
Priority:	high
Version:	unspecified	CC:	tkorbar
Target Milestone:	---	Keywords:	Security
Target Release:	---
Hardware:	All
OS:	Linux
Whiteboard:
Fixed In Version:	xterm 366	Doc Type:	If docs needed, set a value
Doc Text:	A flaw was found in xterm. A specially crafted sequence of combining characters causes an out of bounds write leading to arbitrary code execution. The highest threat from this vulnerability is to confidentiality, integrity, as well as system availability.	Story Points:	---
Clone Of:		Environment:
Last Closed:	2021-02-18 19:02:54 UTC	Type:	---
Regression:	---	Mount Type:	---
Documentation:	---	CRM:
Verified Versions:		Category:	---
oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
Embargoed:
Bug Depends On:	1927564, 1927565, 1927566, 1927567, 1927568, 1927569, 1927570
Bug Blocks:	1927561

Description Doran Moppert 2021-02-11 01:13:00 UTC

A crash was reported in xterm prior to patch #366 when processing a specially crafted sequence of combining characters.  The cause is an out of bounds write, which may be exploitable to cause arbitrary code execution.

https://www.openwall.com/lists/oss-security/2021/02/09/7
https://invisible-island.net/xterm/xterm.log.html

Comment 1 Doran Moppert 2021-02-11 01:24:06 UTC

Created xterm tracking bugs for this issue:

Affects: fedora-all [bug 1927570]

Comment 4 Doran Moppert 2021-02-11 02:57:29 UTC

Mitigation:

This vulnerability can be mitigated by disabling UTF-8 support in XTerm configuration.  An entry such as "XTerm.vt100.utf8: false" in Xresources will disable UTF-8.  This can be set as a system default in /etc/X11/Xresources, or per-user in ~/.Xresources.

Note that this setting can still be overridden if xterm is invoked with the "-u8" command line option, so the mitigation may not protect all use cases.

Comment 5 errata-xmlrpc 2021-02-18 14:54:27 UTC

This issue has been addressed in the following products:

  Red Hat Enterprise Linux 8

Via RHSA-2021:0611 https://access.redhat.com/errata/RHSA-2021:0611

Comment 6 Product Security DevOps Team 2021-02-18 19:02:54 UTC

This bug is now closed. Further updates for individual products will be reflected on the CVE page(s):

https://access.redhat.com/security/cve/cve-2021-27135

Comment 7 errata-xmlrpc 2021-02-22 11:12:12 UTC

This issue has been addressed in the following products:

  Red Hat Enterprise Linux 7

Via RHSA-2021:0617 https://access.redhat.com/errata/RHSA-2021:0617

Comment 8 errata-xmlrpc 2021-02-24 07:45:25 UTC

This issue has been addressed in the following products:

  Red Hat Enterprise Linux 8.1 Extended Update Support

Via RHSA-2021:0650 https://access.redhat.com/errata/RHSA-2021:0650

Comment 9 errata-xmlrpc 2021-02-24 07:54:50 UTC

This issue has been addressed in the following products:

  Red Hat Enterprise Linux 8.2 Extended Update Support

Via RHSA-2021:0651 https://access.redhat.com/errata/RHSA-2021:0651